Low voltage high speed CMOS line driver without tail current source

Abstract

The present invention is directed to electrical circuits and techniques thereof. More specifically, an embodiment of the present invention provides a line driver with transistors directly coupled to the ground, and a bias voltage is coupled common mode resistors of the line driver. There are other embodiments as well.

What is claimed is: 
     
       1. A differential amplifier device comprising:
 a voltage supply, the voltage supply being characterized by a first voltage level; 
 a common voltage source; 
 a first load resistor and a second load resistor, the first load resistor and the second load resistor being characterized by a first resistance value; 
 a first common resistor and a second common resistor, the first common resistor being characterized by a second resistance value, the second resistance value being higher than the first resistance value, the first common resistor being configured in series with the second common resistor, the common voltage source being coupled between the first common resistor and the second common resistor; 
 a first voltage input and a second voltage input; 
 a first switch comprising a first gate and a first drain and a first source, the first gate being coupled to the first voltage input, the first drain being coupled to the first load resistor and the first common resistor, the first source being coupled to a ground terminal; and 
 a second switch comprising a second gate and a second drain and a second source, the second gate being coupled to the second voltage input, the second drain being coupled to the second load resistor and the second common resistor, the second source being coupled to the ground terminal; 
 wherein the differential amplifier being characterized by a swing voltage, the swing voltage being substantially equal to the first voltage level; 
 wherein the common voltage source comprises a voltage divider, the voltage divider comprises a pair of resistors characterized by predetermined resistance values. 
 
     
     
       2. The device of  claim 1  wherein the first switch comprises an NMOS transistor. 
     
     
       3. The device of  claim 1  wherein the second resistor value is at least 100 times greater than the first resistor value. 
     
     
       4. A line driver apparatus comprising:
 a bias resistor; 
 a bias current source coupled to the bias resistor; 
 an amplifier comprising a first input terminal and a second input terminal and output terminal, the first input terminal being coupled to the bias current source and the bias resistor; 
 a pre driver module, the pre driver module being coupled to the output terminal, the pre driver module being configured to provide a first voltage input and a second voltage input; 
 a voltage supply, the voltage supply being characterized by a first voltage level; 
 a common voltage source; 
 a first load resistor and a second load resistor, the first load resistor and the second load resistor being characterized by a first resistance value; 
 a first common resistor and a second common resistor, the first common resistor and the second common resistor being characterized by a second resistance value, the second resistance value being higher than the first resistance value, the first common resistor being configured in series with the second common resistor, the common voltage source being coupled between the first common resistor and common resistor the second input terminal of the amplifier; 
 a first switch comprising a first gate and a first drain and a first source, the first gate being coupled to the first voltage input, the first drain being coupled to the first load resistor and the first common resistor, the first source being coupled to a ground terminal; and 
 a second switch comprising a second gate and a second drain and a second source, the second gate being coupled to the second voltage input, the second drain being coupled to the second load resistor and the second common resistor, the second source being coupled to the ground terminal; 
 wherein the line driver being characterized by a swing voltage, the swing voltage being substantially equal to the first voltage level. 
 
     
     
       5. The apparatus of  claim 4  wherein the pre driver module comprises a third switch coupled to the output terminal of the amplifier. 
     
     
       6. The apparatus of  claim 4  wherein the pre driver comprises a pair of PMOS transistors coupled to a pair of input signals. 
     
     
       7. The apparatus of  claim 5  wherein the pair of PMOS transistors are respectively coupled to a pair of pre driver resistors. 
     
     
       8. The apparatus of  claim 5  wherein the third switch is coupled to the voltage supply. 
     
     
       9. The apparatus of  claim 4  wherein the bias resistor and the bias current source are configured in series. 
     
     
       10. The apparatus of  claim 4  wherein the bias resistor is configured between the voltage supply and the bias current source. 
     
     
       11. A line driver apparatus, comprising:
 a voltage supply, the voltage supply being characterized by a first voltage level; 
 a common voltage source comprising a first resistor and a second resistor configured in series, the first resistor and the second resistor being characterized by a predetermined resistance ratio, a common voltage terminal being coupled between the first resistor and the second resistor; 
 a first load resistor and a second load resistor, the first load resistor and the second load resistor being characterized by a first resistance value; 
 a first common resistor and a second common resistor, the first common resistor being characterized by a second resistance value, the second resistance value being higher than the first resistance value, the first common resistor being configured in series with the second common resistor, the common voltage terminal being coupled between the first common resistor and the second common resistor; 
 a first voltage input and a second voltage input; 
 a first switch comprising a first gate and a first drain and a first source, the first gate being coupled to the first voltage input, the first drain being coupled to the first load resistor and the first common resistor, the first source being directly coupled to a ground terminal; and 
 a second switch comprising a second gate and a second drain and a second source, the second gate being coupled to the second voltage input, the second drain being coupled to the second load resistor and the second common resistor, the second source being directly coupled to the ground terminal. 
 
     
     
       12. The apparatus of  claim 11  wherein the first resistor is coupled to the voltage supply and the second resistor is coupled to the ground terminal. 
     
     
       13. The apparatus of  claim 11  wherein the first switch comprises an NMOS transistor. 
     
     
       14. The apparatus of  claim 11  wherein the differential amplifier is characterized by a swing voltage, the swing voltage being substantially equal to the first voltage level.